An airlift pumping mechanism is a type of pumping apparatus that uses compressed air as the propellant for pumping fluid up a riser tube. The structure involved is simple and requires little maintenance for reliable operation. So that the mechanism has wide applications in fields such as mining, oil & gas exploration, agriculture, and wastewater treatment.
WO2012/046159A1 discloses a system that uses an airlift pumping mechanism in an apparatus for applications such as brewing beverages. An embodiment is shown in FIG. 1. The apparatus is generally comprised of a container 30, an air pump 50, a riser tube 40, an infuser 70, a heater 60, a sensor 62, and a control unit 82. The fluid 20 (e.g. water) and ingredients 25 (such as, tea) for the brewing process are placed in the container 30 and infuser 70, respectively. The pumping action is achieved by first activating the air pump 50 to produce compressed air. The generated air will force the fluid 20 up the riser tube 40 and released over the ingredients 25 in the infuser 70 (in the direction of arrow A1). Once the infuser 70 is filled with the fluid 20, the fluid 20 then returns to the container 30 to form a circulative brewing process. The heater 60 located at the bottom 36 of the container 30 provides temperature control during the brewing process. The control unit 82 controls the brewing process according to sensed signals from the sensor 62 and reference signal REF2.
However, there are some problems with the airlift pumping mechanism in WO2012/046159A1. Specifically, firstly, the pumping efficiency is very low at low residual water volumes (i.e. low liquid levels). The pumping efficiency of the airlift pumping mechanism is in proportion to the submergence ratio defined as Hw/Hs, wherein Hw is the liquid level within the riser tube and Hs is the total length of the riser tube. In general, the higher the submergence ratio is, the higher the pumping efficiency will be. In other words, low water levels, as shown in FIG. 2 when compared with FIG. 1, would produce low submergence ratios that would lead to low pumping efficiency or even zero water flow. Such flow rate limitations would negatively impact on the brewing results produced by the system. Secondly, the shape of an air collector has a negative effect on the structural configuration. To more effectively collect and stream the compressed air into the riser tube, a fan-shaped air collector may be used at the lower end of the riser tube (see the sector end 41 in FIG. 1). However, the horizontal spread of the air collector requires certain amount of clearance in space and may interfere with other structural components, thereby limiting options in structural configuration of the system. Furthermore, there is residual fluid remaining inside the air channel. As shown in FIG. 3, the compressed air travels along the air channel P1 and enters the bottom of the container through an opening 51. A one-way valve 55 is placed between the air channel P1 and the opening 51 to prevent backflows of the fluid 20 into the air channel. However, a small amount of residual water may get trapped in the small conduit between the opening 51 and the one-way valve 55. The reason is that even if the container is drained after use, small liquid drops may still remain inside the container and aggregate at the opening. If not completed dried, such residual water may pose a sanitary concern.